Throughout this application, citations for various Publications are provided within parentheses in the text. The disclosures of these publications are hereby incorporated in their entirety by reference into this application in order to more fully describe the state of the art to which this invention pertains.
The development of resistance to cytotoxic agents is a significant problem in cancer therapy. In multiple drug resistance (MDR), cells become cross-resistant to unrelated chemotherapeutic agents. The MDR phenotype is associated with decreased drug retention and over-expression of P-glycoprotein (Pgp), a membrane protein which mediates drug efflux. Pgp expression and chemotherapeutic resistance has also been functionally associated in leukemias and breast cancer, ovarian cancer and neuroblastoma.
Methods of overcoming multidrug resistance have primarily utilized agents which "reverse" the phenotype by increasing intracellular drug concentrations in resistant cells. The reversal agents act presumably by inhibiting P-glycoprotein-mediated drug efflux. However, reversal agents now in clinical trials, such as verapamil and cyclosporin A, have limited utility due to toxic effects. More active agents with fewer toxic effects are needed.
MDR reversal agents include various calcium channel blockers, such as verapamil, calmodulin Inhibitors, steroid hormones and nonionic detergents. The present invention provides compounds which are selectively toxic to drug-resistant cells in the absence of resistant drugs. The present invention demonstrates "synergism" and "collateral sensitivity" of MDR cells toward certain compounds related to ardeemin. Since drug concentrations needed to mediate collateral sensitivity often exceed that for MDR reversal, more efficient methods of preparation are necessary to provide adequate supplies of material. The selective cytotoxicity of these agents to MDR cells may then be exploited clinically.
The present invention provides new compounds and new methods for the treatment of cancer cells, not only through MDR reversal but also through collateral sensitivity and "quantitated synergism." The new compounds include analogues of amauromine (1; Takase, S.; Iwami, M.; Ando, T.; Okamoto, M.; Yoshida, K.; Horiai, H.; Kohsaka, M.; Aoki, H.; Imanaka, H., J. Antibiot., 1984, 37, 1320; Takase, S.; Kawai, Y.; Uchida, I.; Tanaka, H.; Aoki, H., Tetrahedron, 1985, 41, 3037; Takase, S.: Itoh, Y.: Uchida, I.; Tanaka, H.; Aoki, H., Tetrahedron, 1986, 42, 5887), ardeemin (2; Karwowski, J. P.; Jackson, M.; Rasmussen, R. R.; Humphrey, P. E.; Poddig, J. B.; Kohl, W. L.; Scherr, M. H.; Kadam, S.; McAlpine, J. B., J. Antibiot., 1993, 46, 374; Hochlowski, J. E.; Mullally, M. M.; Spanton, S. G.; Whittern, D. N.; Hill, P.; McAlpine, J. B., J. Antibiot., 1993, 46, 380) and 5-N-acetylardeemin (3). All of these analogues are members of a burgeoning class of biologically active indole alkaloids (including aszonalenin (Kimura, Y.; Hamasaki, T.; Nakajima, H.; Isogai, A., Tetrahedron Lett., 1982, 23, 225) roquefortine (Scott, P. M.; Merrien, M. -A.; Polonsky, J., Experientia, 1976, 32, 140; Scott, P. M.; Polonsky, J.; Merrien, M. -A., J. Agric. Food Chem., 1979, 27, 201) and the flustramines (see, for example, Carle, J. S.; Christophersen, C., J. Am. Chem. Soc., 1979, 101, 4012; Carle, J. S.; Christophersen, C., J. Org. Chem., 1981, 46, 3440) featuring a hexahydropyrrolo[2,3-b]indole nucleus, substituted at the benzylic ring junction with a 1,1-dimethylallyl ("reverse-prenyl") group. In a complementary family of alkaloids (gypsetin), the reverse-prenyl group is found at the 2-position of the indoline. (Shinohara, C.; Hasumi, K.; Takei, Y.; Endo, A., J. Antibiot., 1994, 47, 163; Brevianamide, E.; Birch, A. J.; Wright, J. J., Tetrahedron, 1970, 26, 2329.)
Amauromine is a vasodilator, apparently operating through calcium antagonism. (Takase, S.; Iwami, M.; Ando, T.; Okamoto, M.; Yoshida, K.; Horiai, H.; Kohsaka, M.; Aoki, H.; Imanaka, H., J. Antibiot., 1984, 37, 1320) Compound 3 (FIG. 1) is one of the most potent known agents for reversal of multidrug resistance, as measured against KBV-1 (vinblastine resistant) tumor cell lines. (Karwowski, J. P.; Jackson, M.; Rasmussen, R. R.; Humphrey, P. E.; Poddig, J. B.; Kohl, W. L.; Scherr, M. H.; Kadam, S.; McAlpine, J. B., J. Antibiot., 1993, 46, 374; Hochlowski, J. E.; Mullally, M. M.; Spanton, S. G.; Whittern, D. N.; Hill, P.; McAlpine, J. B., J. Antibiot., 1993, 46, 380) A different method of preparing amauromine via a thio-Claisen rearrangement has been disclosed (Takase, S.: Itoh, Y.: Uchida, I.; Tanaka, H.; Aoki, H., Tetrahedron, 1986, 42, 5887), but is low-yielding, lacks satisfactory stereocontrol, and is not applicable to preparing 3.
The present invention provides compounds, including analogues and hybrids of ardeemin, amauromine and gypsetin, and compositions thereof, which are useful, alone or in conjunction with anticancer drugs, as MDR reversal, collateral sensitive and quantitated synergistic agents, to treat cancer and prevent the emergence of the MDR phenotype. The invention also provides a method of preparation for N-acylardeemins, previously unavailable except by fermentation, and methods of inhibiting growth of conventional p-glycoprotein MDR and Topo II gene-mutated MDR cells using ardeemin analogues and hybrids.